Tapered thread connection pair

ABSTRACT

A tapered thread connection pair comprises an external thread and an internal thread. The external thread comprises an outside helical surface and a first end helical surface, the shape of the outside helical surface is the same as that of a spiral outside surface of a solid of revolution, and the shape of the first end helical surface is the same as that of a spiral end surface of the end having a moving direction that is the same as an axial movement direction of the solid of revolution. The internal thread comprises an inside helical surface and a second end helical surface. The shape of the inside helical surface is the same as that of the spiral outside surface of the solid of revolution.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of international Patent ApplicationNo. PCT/CN2016/107049 with a filing date of Nov. 24, 2016, designating,the United States, and further claims priority to Chinese PatentApplication No. 201510828096.5 with a filing date of Nov. 24, 2015. Thecontent of the aforementioned applications, including any interveningamendments thereto, are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to the field of thread connectionstructure, and more particularly to a tapered thread connection pair.

BACKGROUND OF THE PRESENT INVENTION

A screw thread is a ridge wrapped around a cylinder or cone in the formof a helix. A screw thread is one of the first standardized mechanicalstructure elements, which has been widely used in all kinds of fields.The screw thread can be divided into many species and types with the onedefined on a cylinder being called a straight thread, the one defined ona cone being called a tapered thread, and the one defined on an endsurface of a cylinder or a truncated cone being called a plane thread.The screw thread defined on an outer circular surface of a main body iscalled an external thread, the screw thread defined on an inner circularsurface of a main body is called an internal thread, and the screwthread defined on an end surface of a main body is called an end thread.The screw thread with its rotation direction and helix orientationfollowing the left hand grip rule is called a left-handed thread, andthe screw thread with its rotation direction and helix orientationfollowing the right hand grip rule is called a right-handed thread. Thescrew thread with a single helix on a cross section of a main body iscalled a single-start thread, the screw thread with double helixes iscalled a double start thread, and the screw thread with multiple helixesis called a multi-start thread. The screw thread with a triangular crosssection is called a triangular thread, the screw thread with atrapezoidal cross section is called a trapezoidal thread, the screwthread with a rectangular cross section is called a rectangular thread,and the screw thread with a zigzagging cross section is called azigzagging thread. The screw thread used for fastening connection iscalled a fastening connection thread, the screw thread mainly used fortransmission is called a transmission connection thread, and the screwthread used for conduit connection is called a conduit connectionthread.

The screw thread of a fastener is the fastening connection thread, whichis usually a cylinder thread with a triangle cross section, and isusually a right-handed thread while a left-handed thread is used forspecial use. The screw thread of a fastener is usually a single-startthread while a double-start or multi-start thread is used for celeritydisassembly and assembly. The screw thread of a fastener comprises ascrew thread pair, i.e. an internal thread and an external thread. Thecoupling nature of the screw thread pair is determining by therequirements of the connection system. The basic requirements of thefastener on the screw thread are loading-bearing and self-lockingcapability instead of transmission capability. The basic condition forself-locking thread is that an equivalent friction angle is no less thana lead angle. The value of an equivalent friction angle is related to athread angle, the bigger the thread angle is, the bigger the equivalentfriction angle is, and the more beneficial to self-locking that is thefundamental cause of the thread angle of fastener being 60° C. The wedgethread proposed in recent years, also called “Spiralock nut”, is animprovement to both of the metric screw threads and English screwthreads, aiming at improving the self-locking capability of the screwthread defined on a fastener. The metric screw threads include ISOmetric threads (M screw threads), aerospace metric threads (MJ screwthreads), small metric threads (S screw threads) and Russian screwthreads (MR screw threads), etc. the English screw threads includeunified screw threads (UN screw threads), aerospace inch threads (UNJscrew threads). Whitworth threads and so on. In the English screwthreads the thread angle is 60° C. except that of the Whitworth thread.

The key factor for unthreading problem of the threaded fastener is thestructure of the screw thread. In this case, the American engineersre-designed the geometric shape of the screw thread after researching onthe shape the screw and force, loaded on the fastener. At the end of1970s, the technology of screw thread called “Spiralock” was proposed.The structure of “Spiralock” thread is that a wedge surface with a 30°C. inclination is defined at the root of a negative thread (internaltriangular thread, i.e. female thread). When the bolt is coupled withthe nut, a teeth portion of the external thread of a standard bolt abutsagainst the wedge incline of the internal thread, and hence generatinginterference screw locking to increase locking force. The increase ofthe locking force is due to the change of the thread angle which hencemakes the angle between the normal force between the internal andexternal threads and an axis of the bolt to be 60° C. instead of 30° C.,i.e. the angle of a standard thread. Obviously, the normal force of“Spiralock” thread is significantly greater than fasten stress. Thus,the locking friction generated is greatly increased. The technical leveland professional direction are always focused on thread angles inresearching on and solving the unthreading problem of threadedfasteners. The wedge threads are no exception. Moreover, the wedgethreads are only partial variation of triangle threads. There is nowedge thread pair in use, and the wedge thread can be only used asfemale which couples with an external triangle thread. The locking forceof the wedge thread is determined by the thread angle, and the loadingforce and self-locking capability of the wedge thread is the same asthose of conventional thread techniques. The bolt or nut in the priorart has the defect of being easy unthreaded. With frequent shock of thedevice, the gap between the connection elements is increased, and thebolt and nut are hence unthreaded, or even fell out. In this case, it iseasy for connectors in mechanical connection to depart from each other,or even cause security incident.

Aiming at the defects in the prior art, there has been a long-termexploration, and kinds of solutions have been proposed. For example,Chinese patent No. 201410521899.1 discloses a lock nut with changedthread pattern which comprises a nut body with an internal thread, aspiraling-up conic surface is defined on crest of the internal thread.As a preferred embodiment, an angle between a generatrix of the conicsurface and center axis of the internal thread is 30° C. As a preferredembodiment, two ends of the nut body are an entrance and an exit of thebolt respectively. The entrance of the bolt extends outwardly to form astep, an inclination of a step surface of the step is S, an edge of theexit of the bolt is an inclined surface with an inclination of D. As animprovement of above preferred embodiment, the S is ranged from 20° C.to 30° C., and the D is 30° C.

Above solution an improvement to a certain extent in solving the problemof easy looseness of connection between thread connection pair in priorart. However, there are still the problems of low bonding strength, lowself-locking capability and low loading capability in above solution.

SUMMARY OF PRESENT INVENTION

Aiming at above technical problems, an object of the disclosure is toprovide a tapered-thread connection pair with professional design,simple structure, good connection performance, high self-lockingcapability. The key point of the disclosure is the structure of taperedthreads of the connection pair.

In order to achieve above objects, technical solutions of the presentdisclosure are as follows:

A tapered-thread connection pair, comprises an external thread and aninternal thread in a threaded connection with each other; the externalthread is defined on a main body, and the internal thread is defined ina connection hole; the external thread comprises an outside helicalsurface and a first end helical surface; a shape of the outside helicalsurface is the same as a shape of a lateral surface of a first solid ofrevolution formed by using a first right trapezoid as a generatrix,rotating uniformly around a cathetus of the first right trapezoid whichis coincident with a center axis of the main body, and synchronously,axially and uniformly moving the first right trapezoid along the centeraxis of the main body; a shape of the first end helical surface is thesame as a shape of helical end surface with a same direction as an axialmoving direction of the first solid of revolution; each rotation of thetapered external thread is in a geometrical shape of a helical externalcone; the outside helical surface is a helical external conical surfaceof the helical external cone; the first end helical surface is a helicalend surface of the helical external cone; a first cone angle is formedbetween the outside helical surfaces; the internal thread comprises aninside helical surface and a second end helical surface; a shape of theinside helical surface is the same as a shape of a lateral surface of asecond solid of revolution formed by using a second right trapezoid as ageneratrix, rotating uniformly around a cathetus of the second righttrapezoid which is coincident with a center axis of the connection hole,and synchronously, axially and uniformly moving the second righttrapezoid along the center axis of the connection hole; each rotation ofthe tapered internal thread is in a geometrical shape of a helicalinternal cone; the inside helical surface is a helical internal conicalsurface of the helical internal cone; the second end helical surface isa helical end surface of the helical internal cone; a second cone angleis formed between the inside helical surfaces. When the tapered-threadconnection pair in the present disclosure is in use, the outside andinside helical surfaces are matched with each other and are sized untilinterference fitting to achieve the technical performances such as theconnection property, locking property, anti-loosening performance,loading capability, sealing performance and so on. Namely, the outsideand inside helical surfaces are sized under the guiding of the helixuntil interference contacting, so that the technical performances suchas the connection property, locking property, anti-looseningperformance, loading capability, sealing performance and so on areachieved. It should be noted that the matching between the internal andexternal cones is the matching between the outside and inside conicalsurfaces in fact. In other words, when the internal and external conesmatch with each other, the matching surfaces between them are conicalsurfaces. In order to realize self-locking, the internal and externalcones must satisfy some requirements which are relative to the conicalsurface and conical degree (cone angle) of the cone and are irrelevantto the end surface of the cone. However, it does not mean that a conewith any conical degree can be self-locked. In order words, it does notmean a cone with any cone angle can be self-locked. When the internaland external cones match with each, they can be self-locked only whenthe first cone angle of the outside helical surfaces and the second coneangle of the inside helical surfaces are in a certain rang. Therefore,the technical performances such as the loading capability, self-lockingcapability, anti-loosening performance, sealing performance and so onare irrelevant to the external helix guiding angle and internal helixguiding angle and are relative to the first cone angle of the outsidehelical surfaces and the second cone angle of the inside helicalsurfaces. In other words, the technical performances such as the loadingcapability, self-locking capability, anti-loosening performance, sealingperformance and so on are mainly determined by the first cone angle ofthe outside helical surfaces and the second cone angle of the insidehelical surfaces, and are also relative to friction factors of the mainbody and the connection hole to some extent.

In above tapered-thread connection pair, when the first right trapezoidgoes through one rotation, a distance that the first right trapezoidaxially moves is equal to or greater than a length of the cathetus ofthe first right trapezoid; and when the second right trapezoid goesthrough one rotation, a distance that the second right trapezoid axiallymoves is equal to or greater than a length of the cathetus of the secondright trapezoid. This structure ensures the outside and inside helicalsurfaces are enough in length, and enough strength is ensured when theoutside helical surface matches with the inside helical surface.

In above tapered-thread connection pair, when the first right trapezoidgoes through one rotation, a distance that the first right trapezoidaxially moves is equal to a length of the cathetus of the first righttrapezoid; and when the second right trapezoid goes through onerotation, a distance that the second right trapezoid axially moves isequal to a length of the cathetus of the second right trapezoid. Thisstructure ensures the outside helical surface is enough in length, andenough strength is ensured when the outside helical surface matches withthe metric thread or inside helical surface.

In above tapered-thread connection pair, both the outside helicalsurface and the first end helical surface are continuous helicalsurfaces or non-continuous helical surfaces; and both the inside helicalsurface and the second end helical surface are continuous helicalsurfaces or non-continuous helical surfaces. Preferably, both theoutside helical surface and the first end helical surface are continuoushelical surfaces; and both the inside helical surface and the second endhelical surface are continuous helical surfaces.

In above tapered-thread connection pair, a first transitional guidingsurface is arranged between the outside helical surface and the firstend helical surface on a same rotation. The first transitional guidingsurface, as a helical end surface of the external cone, is designedbased on the first end helical surface and is a variation of the firstend helical surface to facilitate the matching between the internal andexternal threads and to be used as a design and manufacture rule. Thefirst transitional guiding surface facilitates the manufacture of theoutside helical surface and the first end helical surface, protects theinternal and external threads from interference when they matching witheach other and makes the matching more effective. A second transitionalguiding surface is arranged between the inside helical surface and thesecond end helical surface on a same rotation. The second transitionalguiding surface, as a helical end surface of the external cone, isdesigned based on the second end helical surface and is a variation ofthe second end helical surface to facilitate the matching between theinternal and external threads and to be used as a design and manufacturerule. The second transitional guiding surface facilitates themanufacture of the outside helical surface and the second end helicalsurface, protects the internal and external threads from interferencewhen they matching with each other and makes the matching moreeffective. A helical external thread line is formed between two adjacentoutside helical surfaces. A vertical distance between the highest pointand the lowest point of the external thread line, i.e. a height of theexternal helix guiding angle, is much less than a height of thread angleof the screw thread in prior art. Such comparison is based on theprerequisite that the pitch, of the external thread in the presentdisclosure is the same as that of the external thread in prior art. Thepractical meaning is that the semi-cone angle of the first cone angle ofthe external helical surface is less than thread bottom angle of thetooth-type thread. The height of the thread angle refers to threadheight or thread depth of tooth-type thread, i.e. metric internalthread. An external helix guide angle (β1) is defined as an anglebetween an inclined surface formed by a highest point and a lowest pointof the external thread line and an axis of the tapered thread. The screwthread is with a more compact structure, higher strength, higher loadingcapability and better mechanical sealing performance, and a physicalspace for manufacturing the tapered external thread is larger. A helicalinternal thread line is formed between two adjacent outside helicalsurfaces. A vertical distance between the highest point and the lowestpoint of the internal thread line, i.e. a height of the internal helixguiding angle, is much less than a height of thread angle of the screwthread in prior art. Such comparison is based on the prerequisite thatthe pitch of the internal thread in the present disclosure is the sameas that of the internal thread in prior art. The practical meaning isthat the semi-cone angle of the second cone angle of the internalhelical surface is less than thread bottom angle of the tooth-typethread. The height of the thread angle refers to thread height or threaddepth of tooth-type thread, i.e. metric internal thread. An internalhelix guide angle (β2) is defined as an angle between an inclinedsurface formed by a highest point and a lowest point of the internalthread line and an axis of the tapered thread. The screw thread is witha more compact structure, higher strength, higher loading capability andbetter mechanical sealing performance, and a physical space formanufacturing the tapered internal thread is larger.

In above tapered-thread connection pair, one end of the main body is aninsertion end to be inserted into the connection hole; a big end in eachrotation of the first end helical surface is orientated towards theinsertion end of the main body; an orientation of a big end in eachrotation of the second end helical surface is the same as that of thefirst end helical surface. The outside helical surface and the insidehelical surface are coupled with interference fit. Namely, a spiraldirection of the outside helical surface is the same as that of theinside helical surface, and the orientations of their big ends are bothtowards the insertion end. The fastening function is realized throughthe interference fit between the outside and inside helical surfaces.

In above tapered-thread connection pair, one end of the main body is aninsertion end to be inserted into the connection hole; a small end ineach rotation of the first end helical surface is orientated towards theinsertion end of the main body; an orientation of small end in eachrotation of the second end helical surface is the same as that of thefirst end helical surface. The outside helical surface and the insidehelical surface are coupled with interference fit. Namely, a spiraldirection of the outside helical surface is the same as that of theinside helical surface, and the orientations of their small ends areboth towards the insertion end. The fastening function is realizedthrough the interference fit between the outside and inside helicalsurfaces.

In above tapered-thread connection pair, one end of the main body is aninsertion end to be inserted into the connection hole; a big end in eachrotation of the first end helical surface is orientated towards theinsertion end of the main body; an orientation of a big end in eachrotation of the second end helical surface is opposite to that of thefirst end helical surface. A portion where an intersection line runningthrough the inside helical surface and the second end helical surface ona same rotation of the connection hole locates and the outside helicalsurface of the main body are coupled with interference fit. Namely, aspiral direction of the outside helical surface is opposite to that ofthe inside helical surface, and the orientations of the big ends of theoutside helical surfaces are towards the insertion end. The fasteningfunction is realized through the interference fit between the portionwhere an intersection line running through the inside helical surfaceand the second end helical surface on a same rotation of the connectionhole locates and the outside helical surface of the main body.

In above tapered-thread connection pair, one end of the main body is aninsertion end to be inserted into the connection hole; a small end ineach rotation of the first end helical surface is orientated towards theinsertion end of the main body; an orientation of a small end in eachrotation of the second end helical surface is opposite to that of thefirst end helical surface. A portion where an intersection line runningthrough the inside helical surface and the second end helical surfacelocates and the outside helical surface are coupled with interferencefit. Namely, a spiral direction of the outside helical surface isopposite to that of the inside helical surface, and the orientations ofthe small ends of the outside helical surfaces are towards the insertionend. The fastening function is realized through the interference fitbetween the portion where an intersection line running through theinside helical surface and the second end helical surface locates andthe outside helical surface of the main body.

In above tapered-thread connection pair, a head portion with a diametergreater than that of the main body is arranged at an end of the mainbody. The main body can be a bolt without the head portion with adiameter greater than that of the main body. The connection hole is aconnection hole defined on workpiece, such as a nut.

Compared with prior art, the tapered-thread connection pair in thisdisclosure have the following advantageous of professional design,simple structure, easy operation, high locking force, high loadingcapability, good anti-loosening property, good mechanical sealingproperty, good stability and high self-locking capability. The fasteningand connection functions can be realized by sizing between the internaland external cones until they are coupling with interference fit. Thetapered-thread connection pair is capable of avoiding unthreading.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic exploded view of a tapered-thread connection pairaccording to the present invention;

FIG. 2 is a schematic assembled view of the tapered-thread connectionpair according, to the present invention;

FIG. 3 is a schematic assembled view of a tapered-thread connection pairaccording to the present invention;

FIG. 4 is a schematic assembled view of a tapered-thread connection pairaccording to the present invention; and

FIG. 5 is a schematic assembled view of a tapered-thread connection pairaccording to the present invention.

In the drawings, 1—main body; 11—outside helical surface; 12—first endhelical surface; 13—first transitional guiding surface; 2—connectionhole; 21—inside helical surface; 22—second end helical surface;23—second transitional guiding surface; 3—nut; 4—external thread line;5—internal thread line; 6—external thread; 61—head portion; 7—internalthread; α1—first cone angle; α2—second cone angle; β1—external helixguiding angle; and β2—internal helix guiding angle.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention is further described below in combination withdrawings and embodiments.

Embodiment 1

As shown in FIG. 1 and FIG. 2, a tapered-thread connection pair,comprises an external thread 6 and an internal thread 7 in a threadedconnection with each other. The external thread 6 is defined on a mainbody 1, and the internal thread 7 is defined in a connection hole 2. Ahead portion 61 with a diameter greater than that of the main body 1 isarranged at an end of the main body 1. The connection hole 2 is a screwhole 2 defined in a workpiece such as a nut 3. The external thread 6comprises an outside helical surface 11 and a first end helical surface12. A shape of the outside helical surface 11 is the same as a shape ofa lateral surface of a first solid of revolution formed by using a firstright trapezoid as a generatrix, rotating uniformly around a cathetus ofthe first right trapezoid which is coincident with a center axis of themain body 1, and synchronously, axially and uniformly moving the firstright trapezoid along the center axis of the main body 1. A shape of thefirst end helical surface 12 is the same as a shape of helical endsurface with a same direction as an axial moving direction of the firstsolid of revolution. Each rotation of the tapered external thread 6 isin a geometrical shape of a helical external cone. The outside helicalsurface 11 is a helical external conical surface of the helical externalcone. The first end helical surface 12 is a helical end surface of thehelical external cone. A first cone angle α1 is formed between theoutside helical surfaces 11. The internal thread 7 comprises an insidehelical surface 21 and a second end helical surface 22. A shape of theinside helical surface 21 is the same as a shape of a lateral surface ofa second solid of revolution formed by using a second right trapezoid asa generatrix, rotating uniformly around a cathetus of the second righttrapezoid which is coincident with a center axis of the connection hole2, and synchronously, axially and uniformly moving the second righttrapezoid along the center axis of the connection hole 2. Each rotationof the tapered internal thread 7 is in a geometrical shape of a helicalinternal cone. The inside helical surface 21 is a helical internalconical surface of the helical internal cone. The second end helicalsurface 22 is a helical end surface of the helical internal cone. Asecond cone angle α2 is formed between the inside helical surfaces 21.When the tapered-thread connection pair in the present disclosure is inuse, the outside and inside helical surfaces 11 and 21 are matched witheach other and are sized until interference fitting to achieve thetechnical performances such as the connection property, lockingproperty, anti-loosening performance, loading capability, sealingperformance and so on. Namely, the outside and inside helical surfaces11 and 21 are sized under the guiding of the helix until interferencecontacting, so that the technical performances such as the connectionproperty, locking property, anti-loosening performance, loadingcapability, sealing performance and so on are achieved. It should benoted that the matching between the internal and external cones is thematching between the outside and inside conical surfaces in fact. Inother words, when the internal and external cones match with each other,the matching surfaces between them are conical surfaces. In order torealize self-locking, the internal and external cones must satisfy somerequirements which are relative to the conical surface and conicaldegree (cone angle) of the cone and are irrelevant to the end surface ofthe cone. However, it does not mean that a cone with any conical degreecan be self-locked. In order words, it does not mean a cone with anycone angle can be self-locked. When the internal and external conesmatch with each, they can be self-locked only when the first cone angleα1 of the outside helical surfaces 11 and the second cone angle α2 ofthe inside helical surfaces 21 are in a certain rang. Therefore, thetechnical performances such as the loading capability, self-lockingcapability, anti-loosening performance, sealing performance and so onare irrelevant to the external helix guiding angle β1 and internal helixguiding angle β2 and are relative to the first cone angle α1 of theoutside helical surfaces 11 and the second cone angle α2 of the insidehelical surfaces 21. In other words, the technical performances such asthe loading capability, self-locking capability, anti-looseningperformance, sealing performance and so on are mainly determined by thefirst cone angle of α1 the outside helical surfaces 11 and the secondcone angle α2 of the inside helical surfaces 21, and are also relativeto friction factors of the main body and the connection hole to someextent.

Specifically, when the first right trapezoid goes through one rotation,a distance that the first right trapezoid axially moves is equal to orgreater than a length of the cathetus of the first right trapezoid; andwhen the second right trapezoid goes through one rotation, a distancethat the second right trapezoid axially moves is equal to or greaterthan a length of the cathetus of the second right trapezoid. Thisstructure ensures the outside and inside helical surfaces 11 and 21 areenough in length, and enough strength is ensured when the outsidehelical surface 11 matches with the inside helical surface 21. In thisembodiment, both the outside helical surface 11 and the first endhelical surface 12 are continuous helical surfaces or non-continuoushelical surfaces; and both the inside helical surface 21 and the secondend helical surface 22 are continuous helical surfaces or non-continuoushelical surfaces. Preferably, both the outside helical surface 11 andthe first end helical surface 12 are continuous helical surfaces; andboth the inside helical surface 21 and the second end helical surface 22are continuous helical surfaces.

Further, a first transitional guiding surface 13 is arranged between theoutside helical surface 11 and the first end helical surface 12 on asame rotation. The first transitional guiding surface, 13 as a helicalend surface of the external cone, is designed based on the first endhelical surface 12 and is a variation of the first end helical surface12 to facilitate the matching between the internal and external threadsand to be used as a design and manufacture rule. The first transitionalguiding surface 13 facilitates the manufacture of the outside helicalsurface 11 and the first end helical surface 12, protects the internaland external threads from interference when they matching with eachother and makes the matching more effective. A helical external threadline 4 is formed between two adjacent outside helical surfaces 11. Avertical distance between the highest point and the lowest point of theexternal thread line 4, i.e. a height of the external helix guidingangle β1, is much less than a height of thread angle of the screw threadin prior art. Such comparison is based on the prerequisite that thepitch of the external thread 6 in the present disclosure is the same asthat of the external thread in prior art. The practical meaning is thatthe semi-cone angle of the first cone angle α1 of the external helicalsurface 11 is less than thread bottom angle of the tooth-type thread.The height of the thread angle refers to thread height or thread depthof tooth-type thread, i.e. metric internal thread. An external helixguide angle β1 is defined as an angle between an inclined surface formedby a highest point and a lowest point of the external thread line 4 andan axis of the tapered thread. The screw thread is with a more compactstructure, higher strength, higher loading capability and bettermechanical sealing performance and a physical space for manufacturingthe tapered external thread is larger. A second transitional guidingsurface 23 is arranged between the inside helical surface 21 and thesecond end helical surface 22 on a same rotation. The secondtransitional guiding surface 23, as a helical end surface of theexternal cone, is designed based on the second end helical surface 21and is a variation of the second end helical surface 21 to facilitatethe matching between the internal and external threads and to be used asa design and manufacture rule. The second transitional guiding surface23 facilitates the manufacture of the outside helical surface 21 and thesecond end helical surface 22, protects the internal and externalthreads from interference when they matching with each other and makesthe matching more effective. A helical internal thread line 5 is formedbetween two adjacent outside helical surfaces 21. A vertical distancebetween the highest point and the lowest point of the internal threadline 5, i.e. a height of the internal helix guiding angle β2, is muchless than a height of thread angle of the screw thread in prior art.Such comparison is based on the prerequisite that the pitch of theinternal thread 7 in the present disclosure is the same as that of theinternal thread in prior art. The practical meaning is that thesemi-cone angle of the second cone angle α2 of the internal helicalsurface 21 is less than thread bottom angle of the tooth-type thread.The height of the thread angle refers to thread height or thread depthof tooth-type thread, i.e. metric internal thread. An internal helixguide angle β2 is defined as an angle between an inclined surface formedby a highest point and a lowest point of the internal thread line 5 andan axis of the tapered thread. The screw thread is with a more compactstructure, higher strength, higher loading capability and bettermechanical sealing performance, and a physical space for manufacturingthe tapered internal thread is larger.

More specifically, one end of the main body 1 is an insertion end to beinserted into the connection hole 2. A big end in each rotation of thefirst end helical surface 12 is orientated towards the insertion end ofthe main body 1. An orientation of a big end in each rotation of thesecond end helical surface 22 is the same as that of the first endhelical surface 12. The outside helical surface 11 and the insidehelical surface 21 are coupled with interference fit. Namely, a spiraldirection of the outside helical surface 11 is the same as that of theinside helical surface 12, and the orientations of their big ends areboth towards the insertion end. The fastening function is realizedthrough the interference fit between the outside and inside helicalsurfaces 11 and 21.

Embodiment 2

As shown in FIG. 3, the structure, principle and implementing method ofthe tapered-thread connection pair in this embodiment are similar tothose of the first embodiment. The differences are that one end of themain body 1 in this embodiment is an insertion end to be inserted intothe connection hole 2, a small end in each rotation of the first endhelical surface 12 is orientated towards the insertion end of the mainbody 1, and an orientation of a small end in each rotation of the secondend helical surface 22 is the same as that of the first end helicalsurface 12. The outside helical surface 11 and the inside helicalsurface 21 are coupled with interference fit. Namely, a spiral directionof the outside helical surface 11 is the same as that of the insidehelical surface 21, and the orientations of their small ends are bothtowards the insertion end. The fastening function is realized throughthe interference fit between the outside and inside helical surfaces 11and 21.

Embodiment 3

As shown in FIG. 4, the structure, principle and in implementing methodof the tapered-thread connection pair in this embodiment are similar tothose of the first embodiment. The differences are that one end of themain body 1 is an insertion end to be inserted into the connection hole2, a big end in each rotation of the first end helical surface 11 isorientated towards the insertion end of the main body 1, an orientationof a big end in each rotation of the second end helical surface 21 isopposite to that of the first end helical surface 11, a portion where anintersection line running through the inside helical surface 21 and thesecond end helical surface 22 on a same rotation of the connection hole2 locates and the outside helical surface 11 of the main body 1 arecoupled with interference fit. Namely, a spiral direction of the outsidehelical surface 11 is opposite to that of the inside helical surface 21,and the orientations of the big ends of the outside helical surfaces 11are towards the insertion end. The fastening function is realizedthrough the interference fit between the portion where an intersectionline running through the inside helical surface 21 and the second endhelical surface 22 on a same rotation of the connection hole 2 locatesand the outside helical surface 11 of the main body 1.

Embodiment 4

As shown in FIG. 5, the structure, principle and implementing method ofthe tapered-thread connection pair in this embodiment are similar tothose of the first embodiment. The differences are one end of the mainbody 1 is an insertion end to be inserted into the connection hole 2, asmall end in each rotation of the first end helical surface 12 isorientated towards the insertion end of the main body 1, an orientationof a small end in each rotation of the second end helical surface 22 isopposite to that of the first end helical surface 12, a portion where anintersection line running through the inside helical surface 21 and thesecond end helical surface 22 locates and the outside helical surface 11are coupled with interference fit. Namely, a spiral direction of theoutside helical surface 11 is opposite to that of the inside helicalsurface 21, and the orientations of the small ends of the outsidehelical surfaces 11 are towards the insertion end. The fasteningfunction is realized through the interference fit between the portionwhere an intersection line running through the inside helical surface 21and the second end helical surface 22 locates and the outside helicalsurface 11 of the main body 1.

The specific embodiments described in this disclosure are exemplaryillustrations to the spirit of the present invention. It is obvious toone of ordinary skill in the art to make modifications and/orsupplementary and/or obtain equivalence using a similar principle underthe teaching of this disclosure without departing from the spirit of thepresent invention or being beyond the protection scope defined in theclaims.

Understandably, the structure of the tapered-thread connection pair canbe widely implemented on all kinds of products, such as bolt and nutwith threaded structures, valves with threaded structure, transmissionmechanisms, containers and so on, as long as the products have internaland external threads coupling with each other.

Although terms such as main body 1, outside surface 11, first endhelical surface 12, first transitional guiding surface 13, connectionhole 2, inside helical surface 21, second end helical surface 22, secondtransitional guiding surface 23, nut 3, external thread line 4, internalthread line 5, external thread 6, head portion 61, internal thread 7,first cone angle α1, second cone angle α2, external helix guiding angleβ1, and internal helix guiding angle β2 and so on have been widely usedin the present disclosure, other terms can also be used alternatively.These terms are only used to better description and illustration theessence of the present invention. It departs from the spirit of thepresent invention to deem it as any limitation of the present invention.

I claim:
 1. A tapered-thread connection pair, comprising an externalthread and an internal thread in a threaded connection with each other;wherein the external thread is defined on a main body, and the internalthread is defined in a connection hole; the external thread comprises anoutside helical surface and a first end helical surface; a shape of theoutside helical surface is the same as a shape of a lateral surface of afirst solid of revolution formed by using a first right trapezoid as ageneratrix, rotating uniformly around a cathetus of the first righttrapezoid which is coincident with a center axis of the main body, andsynchronously, axially and uniformly moving the first right trapezoidalong the center axis of the main body; a shape of the first end helicalsurface is the same as a shape of helical end surface with a samedirection as an axial moving direction of the first solid of revolution;the internal thread comprises an inside helical surface and a second endhelical surface; a shape of the inside helical surface is the same as ashape of a lateral surface of a second solid of revolution formed byusing a second right trapezoid as a generatrix, rotating uniformlyaround a cathetus of the second right trapezoid which is coincident witha center axis of the connection hole, and synchronously, axially anduniformly moving the second right trapezoid along the center axis of theconnection hole; a shape of the second end helical surface is the sameas a shape of helical end surface with a same direction as an axialmoving direction of the second solid of revolution; a first cone angle(α1) is formed between outside helical surfaces; a second cone angle(α2) is formed between inside helical surfaces; the external thread isin a geometrical shape of a helical external cone; the outside helicalsurface is a helical external conical surface of the helical externalcone; the first end helical surface is a helical end surface of thehelical external cone; the internal thread is in a geometrical shape ofa helical internal cone; the inside helical surface is a helicalinternal conical surface of the helical internal cone; the second endhelical surface is a helical end surface of the helical internal cone;the outside and inside helical surfaces are matched with each other andare centralized under the guiding of a helix until interferencecontacting; the internal and external cones are sized until interferencefitting; a helical external thread line is formed between two adjacentoutside helical surfaces; an external helix guide angle (β1) is definedas an angle between an inclined surface formed by a highest point and alowest point of the external thread line and an axis of the externalthread; a helical internal thread line is formed between two adjacentinside helical surfaces; an internal helix guide angle (β2) is definedas an angle between an inclined surface formed by a highest point and alowest point of the internal thread line and an axis of the internalthread; self-locking capability, leak-tightness, loading capability ofthe tapered thread connection pair is determined by values of the firstcone angle (α1) of the outside helical surfaces and a second cone angle(α2) of inside helical surfaces; and fastening and connecting functionsare realized by sizing of internal and external cones until interferencefitting.
 2. The tapered-thread connection pair according to claim 1,wherein when the first right trapezoid goes through one rotation, adistance that the first right trapezoid axially moves is equal to orgreater than a length of the cathetus of the right trapezoid; and whenthe second right trapezoid goes through one rotation, a distance thatthe second right trapezoid axially moves is equal to or greater than alength of the cathetus of the right trapezoid.
 3. The tapered-threadconnection pair according to claim 2, wherein when the first righttrapezoid goes through one rotation, a distance that the first righttrapezoid axially moves is equal to a length of the cathetus of theright trapezoid; and when the second right trapezoid goes through onerotation, a distance that the second right trapezoid axially moves isequal to a length of the cathetus of the right trapezoid.
 4. Thetapered-thread connection pair according to claim 1, wherein both theoutside helical surface and end helical surface are continuous helicalsurfaces or non-continuous helical surfaces; and both the inside helicalsurface and the second end helical surface are continuous helicalsurfaces or non-continuous helical surfaces.
 5. The tapered-threadconnection pair according to claim 1, wherein a first transitionalguiding surface is arranged between the outside helical surface and thefirst end helical surface on a same rotation; and a second transitionalguiding surface is arranged between the inside helical surface and thesecond end helical surface on a same rotation.
 6. The tapered-threadconnection pair according to claim 1, wherein one end of the main bodyis an insertion end to be inserted into the connection hole; a big endin each rotation of the first end helical surface is orientated towardsthe insertion end of the main body; an orientation of a big end in eachrotation of the second end helical surface is the same as that of thefirst end helical surface.
 7. The tapered-thread connection pairaccording to claim 6, wherein a head portion with a diameter greaterthan that of the main body is arranged at an end of the main body; andthe connection hole is a connection hole defined on a nut.
 8. Thetapered-thread connection pair according to claim 1, wherein one end ofthe main body is an insertion end to be inserted into the connectionhole; a small end in each rotation of the first end helical surface isorientated towards the insertion end of the main body; an orientation ofa small end in each rotation of the second end helical surface is thesame as that of the first end helical surface.
 9. The tapered-threadconnection pair according to claim 1, wherein one end of the main bodyis an insertion end to be inserted into the connection hole; a big endin each rotation of the first end helical surface is orientated towardsthe insertion end of the main body; an orientation of a big end in eachrotation of the second end helical surface is opposite to that of thefirst end helical surface.
 10. The tapered-thread connection pairaccording to claim 1, wherein one end of the main body is an insertionend to be inserted into the connection hole; a small end in eachrotation of the first end helical surface is orientated towards theinsertion end of the main body; an orientation of a small end in eachrotation of the second end helical surface is opposite to that of thefirst end helical surface.